1. Field of the Invention
The present invention relates to the treatment of pavement surfaces with rapid setting (RS) asphalt emulsions having "high float" (HF). More specifically, the invention relates to the chip seal surface treatment of pavements with certain novel anionic asphalt emulsions having HFRS properties.
In the chip seal surface treatment of roadways a layer of rapid setting aqueous asphalt emulsion is distributed over the surface either before or after a selected aggregate (i.e., stone) is applied thereto. Upon contact with the chosen aggregate, the RS emulsion rapidly breaks and sets, thereby bonding the aggregate to the asphalt and to the surface. This rapid setting action allows the roadway to be open to traffic rather quickly. In general, an emulsion is qualified for the RS designation if the emulsion has a demulsibility or "break" of 60% or more under defined conditions (ASTM D-977).
It is readily apparent that it would be advantageous to provide a chip seal surface treatment resistant to rain and wear, of increased durability, of reduced high temperature flow, and of improved strength and toughness. In this connection, it is often specified that the asphalt emulsion have "high float" (HF). HF refers to the resistance to flow of the asphalt emulsion residue under defined conditions. The residue is the remainder of the asphalt emulsion after water and other volatiles are distilled off (ASTM D-244). Float tests are normally conducted on the residue at 140.degree. F. by inserting a plug of residue in a standard holed-float. When the plug flows sufficiently, the float will sink and the elapsed time is a measure of the residue's resistance to flow under the force of gravity at 140.degree. F. (ASTM D-139). In general, a Float Test result of 1200 seconds or longer qualifies a rapid setting asphalt emulsion for the HFRS designation. In many cases, asphalt emulsions will qualify as HF or RS but not both. State Highway Departments are increasingly requesting the use of chip seal bituminous emulsions qualifying as both HF and RS.
2. Description of the Prior Art
U.S. Pat. No. 2,679,462 describes a water strip-resistant bituminous composition comprising an alkanol amine ester of a monocarboxylic acid, and optionally, tall oil.
U.S. Pat. No. 2,855,319 describes a paving composition formed as mixture of aggregate and bituminous emulsion in which tall oil soap is the emulsifying agent, and further teaches that such substances as oleic acid when used as emulsifiers, if capable of increasing the high temperature hardness at all, do so only to a limited extent. Furthermore, when used with tall oil soap, such substances tend to produce a softening effect as determined by the Float Test, i.e., such substances tend to decrease high temperature hardness, according to the aforementioned U.S. Pat. No. 2,855,319.
U.S. Pat. No. 3,036,015 teaches the use of organic emulsifiers for oil-in-water emulsions such as water soluble soaps of fatty acids (oleic, palmitic, stearic, lauric, naphthenic and tall oil) prepared by reacting the acid or its glyceride with an alkali.
U.S. Pat. No. 4,433,084 describes a method of making an HFRS emulsion from asphalt, tall oil, base and water.